Platinum, symbol Pt, is a relatively rare, metallic element that is more expensive than gold. The atomic number of platinum is 78. Platinum is one of the transition elements in group 10 of the periodic table. Platinum is the most important of the group of elements called platinum metals. Also included in this group are the metals ruthenium, rhodium, palladium, osmium, and iridium. Platinum metals were probably used in alloyed forms in ancient Greece and Rome and were first mentioned in European literature in the early 16th century. The separation of the other platinum metals from platinum and from each other was accomplished in the early 19th century.
An Italian scientist named Julius Scaliger discovered platinum in 1557, but fairly large quantities were not discovered until around 1750, when the Spaniards discovered it in Peru. Don Antonio de Ulloa wrote the first complete description for the Spaniards and is sometimes credited with the discovery because of the detailed report. The Spaniards named the metal platinum, deriving form their word plata, meaning silver. The ore, called native platinum, usually occurs in beds of gold-bearing sand. Native platinum contains from 60 to 85 % pure platinum. The small, irregular grains that contain the ore also contain other rare metals, such as iridium, osmium, palladium, rhodium, and ruthenium. The grains also contain small amounts of iron, copper, chromium, and titanium. The grains must be introduced to aqua regia, which dissolves the platinum and can then be collected. Platinum is a rare element on Earth. Platinum makes up an estimated 0.01 parts per million in the Earth’s crust. A large nugget of platinum will be found very rarely. The largest nugget ever found was a lump weighing over 21 pounds in Russia. Russia produces the world’s largest supply of platinum-group metals. Other major sources of platinum are located in the Transvaal province in South Africa, Sudbury, Ontario, Colombia, and the United States also has sources of platinum. The United States uses about 475,000 troy ounces of platinum a year. About 1/5 of this comes from its own mines and scrap. The rest is imported largely from Canada, which recovers large quantities of platinum as a byproduct of the nickel industry. In the United States, platinum is found in the gold deposits in California, Nevada, and Oregon. Large amounts also come from the process of refining gold and copper. The first mine solely for platinum in the United States was built in Stillwater County, Montana in 1988.
Platinum is a silver-white metal with a hardness of 4.3. Miners of platinum often refer to it as white gold. It has a high fusing point and is malleable and ductile. Platinum can be hammered as thin as 100 atoms thick. It does not expand very much when heated and has high electrical resistance. Chemically, the metal is relatively inactive and resists attacks by air, water, and single acids. It dissolves slowly in aqua regia, forming chloroplatinic acid. Platinum melts at about 1772° C and boils at about 3827° C. Platinum has oxidation states of +2 and +4. The atomic weight of platinum is 195.09. Platinum has a density of 21.45 g/cm making it one of the densest elements. Platinum is in very few compounds because of its chemical inactivity and is usually alloyed with other metals. Platinum can combine with halogens to form platinum halides. Platinum absorbs large amounts of hydrogen at high temperature. There are six naturally occurring isotopes of platinum: platinum-190, platinum-192, platinum-194, platinum-195, platinum-196, and platinum-198. Platinum-190 is the only radioactive isotope of platinum. Radioactive isotopes of platinum can also be artificially made.
Platinum ranks about 72nd in natural abundance among the elements. Except for the mineral sperrylite, which is found rarely in only a few places, platinum occurs in a metallic state. Because of its chemical inactivity and high fusing point, platinum is valuable for laboratory equipment, such as tongs, funnels, combustion boats, and evaporating dishes. Platinum is also used for contact points in electrical equipment and in instruments used for measuring high temperature. Pacemakers are made of platinum to help avoid corrosion from acids in the body. Platinum is non-magnetic, but when alloyed with cobalt it can form a very strong magnet. One of the best uses of platinum is as a catalyst. A catalyst is a substance